Re: [PATCH v2 net-next] net: generalize skb freeing deferral to per-cpu lists

From: Paolo Abeni <pabeni@redhat.com>
To: Eric Dumazet <eric.dumazet@gmail.com>,
	"David S . Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>
Cc: netdev <netdev@vger.kernel.org>, Eric Dumazet <edumazet@google.com>
Subject: Re: [PATCH v2 net-next] net: generalize skb freeing deferral to per-cpu lists
Date: Tue, 26 Apr 2022 09:38:22 +0200	[thread overview]
Message-ID: <2c092f98a8fe1702173fe2b4999811dd2263faf3.camel@redhat.com> (raw)
In-Reply-To: <20220422201237.416238-1-eric.dumazet@gmail.com>

Hello,

I'm sorry for the late feedback. I have only a possibly relevant point
below.

On Fri, 2022-04-22 at 13:12 -0700, Eric Dumazet wrote:
[...]
> @@ -6571,6 +6577,28 @@ static int napi_threaded_poll(void *data)
>  	return 0;
>  }
>  
> +static void skb_defer_free_flush(struct softnet_data *sd)
> +{
> +	struct sk_buff *skb, *next;
> +	unsigned long flags;
> +
> +	/* Paired with WRITE_ONCE() in skb_attempt_defer_free() */
> +	if (!READ_ONCE(sd->defer_list))
> +		return;
> +
> +	spin_lock_irqsave(&sd->defer_lock, flags);
> +	skb = sd->defer_list;

I *think* that this read can possibly be fused with the previous one,
and another READ_ONCE() should avoid that.

BTW it looks like this version gives slightly better results than the
previous one, perhpas due to the single-liked list usage?

Thanks!

Paolo